The default template includes this:

  {if count($errors) == 1}
    {$errors}
  {else}
    <ul>
    {foreach $errors as $error}
      <li>{$error}</li>
    {/foreach}
    </ul>
  {/if}

If you have 1 error, the output is "Array"

It should be:

  {if count($errors) == 1}
    {$errors[0]}
  {else}
    <ul>
    {foreach $errors as $error}
      <li>{$error}</li>
    {/foreach}
    </ul>
  {/if}

Or shorter:

  {if count($errors)}
    <ul>
    {foreach $errors as $error}
      <li>{$error}</li>
    {/foreach}
    </ul>
  {/if}

Thanks Rolf